Replicative senescence may play an important role in tumor suppression and contribute to organismal aging. Werner syndrome (WS) is a recessive genetic disorder resulting from defects in the WRN gene. HumanSwith WS show many symptoms of accelerated aging, including premature development of several forms of cancer. Cultured cells derived from WS subjects show accelerated senescence compared to normal cells. We hypothesize that WRN is a key regulator for cell growth and senescence. The objective of this proposal is to determine whether and how WRN functions to regulate these processes. Three interrelated studies are proposed. First, sense and antisense WRN cDNAs will be expressed in WS and normal cells, respectively, to study their effects on replicative life span. Second, dominant negative mutants that specifically abolish WRN exonuclease and/or helicase activity will be constructed and expressed in normal cells. The effects of these mutant forms of WRN on genomic stability and replicative life span will be characterized. Third, the expression profile of growth regulatory genes associated with replicative senescence will be examined in normal and WS cells to identify genes that may be differentially expressed between normal and WS cells, and genes that WRN might regulate during replicative senescence. The ultimate goal is to obtain insights into the mechanism(s) by which the accelerated senescence in WS cells is achieved and their relevance to normal cell senescence, and to provide information about the pathway(s) in which WRN might participate and the genes that WRN might regulate to control cell growth and senescence, and ultimately diseases associated with human aging.